Conventionally, as buckles for detachably connecting two connecting objects together, for example, a buckle as disclosed in Patent Document 1 has been known. The buckle is constituted of a plug and a socket. The plug has a tape passing portion, which is an attachment portion provided with a tape insertion hole configured to allow a tape or the like to be inserted therethrough and connected thereto, and a pair of leg portions extending from both end portions, in a width direction, of the tape passing portion to be parallel to each other. Each of the leg portions has an outer leg piece and an inner leg piece, which are elastically deformable, and also has a distal end connection portion for connecting distal ends of the outer leg piece and the inner leg piece to each other. On a pair of distal end connection portions connecting the distal ends of the outer leg piece and the inner leg piece to each other, a pair of engaging protrusions is provided to protrude in a front and back direction. Base end portions of the outer leg piece and the inner leg piece are connected to an arm portion extending from both end portions, in the width direction, of the tape passing portion, toward the protruding of the leg portions to form a generally V-shape. In a valley portion of the arm portion, a guide bar for guiding insertion of the plug is formed to protrude in the protruding direction of the leg portions. The socket, in which the plug is to be fitted, is also provided with a tape passing portion having a tape insertion hole, and a hollow plug fitting portion is provided to integrally extend from one end portion of the tape passing portion. The plug fitting portion is constituted of an upper plate and a lower plate opened at a distal end portion thereof, and also operation opening portions are respectively formed on both side edges, in the width direction, of the upper and lower plates. On a base end side of the operation opening portions, engaged portions are formed to be respectively engaged with the pair of engaging protrusions of the pair of leg portions inserted in the plug fitting portion.
Also, a buckle disclosed in Patent Document 2 has a basic configuration similar to that of Patent Document 1. However, base end portions of portions of the buckle disclosed in Patent Document 2, which correspond to the outer leg piece and the inner leg piece, are not connected to each other. The portion corresponding to the inner leg piece is formed in a thin plate shape, and the base end portion thereof is formed in a generally U-shape and is connected to a base end portion of a guide bar. A U-shaped shallow groove is formed on a base end portion of the guide bar.